Troughs of bok choy stack up vertically at the 30-feet urban farm in Singapore. The veggies rotate along the A-frame to ensure they receive even light.

Courtesy of MNDSingapore.

Singapore is taking local farming to the next level, literally, with the opening of its first commercial vertical farm.

Entrepreneur Jack Ng says he can produce five times as many vegetables as regular farming looking up instead of out. Half a ton of his Sky Greens bok choy and Chinese cabbages, grown inside 120 slender 30-foot towers, are already finding their way into Singapore's grocery stores.

The idea behind vertical farming is simple: Think of skyscrapers with vegetables climbing along the windows. Or a library-sized greenhouse with racks of cascading vegetables instead of books.

Ng's technology is called "A-Go-Gro," and it looks a lot like a 30-foot tall Ferris wheel for plants. Trays of Chinese vegetables are stacked inside an aluminum A-frame, and a belt rotates them so that the plants receive equal light, good air flow and irrigation. The whole system has a footprint of only about 60 square feet, or the size of an average bathroom.

Advocates, whose ranks are growing in cities from New York City to Sweden, say vertical farming has a handful of advantages over other forms of urban horticulture. More plants can squeeze into tight city spaces, and fresh produce can grow right next to grocery stores, potentially reducing transportation costs, carbon dioxide emissions and risk of spoilage. Plus, most vertical farms are indoors, so plants are sheltered from shifting weather and damaging pests.

But is vertical farming just a design fad, or could it be the next frontier of urban agriculture? That depends on your angle — and location.

Implementing these "farmscrapers" on a commercial scale has been challenging, and making them economical has been almost impossible.

It's still up for debate whether vertical farms are more efficient at producing food than traditional greenhouses, says Gene Giacomelli, a plant scientist at the University of Arizona, who directs their the Controlled Environment Agriculture Center.

The limiting factor is light. The total food produced depends on the amount of light reaching plants. Although vertical farms can hold more plants, they still receive just about the same quantity of sunlight as horizontal greenhouses.

"The plants have to share the existing light, and they just grow more slowly." Giacomelli tells The Salt. "You can't amplify the sun."

For American cities, like New York and Chicago, Giacomelli thinks putting plain-old greenhouses on rooftops could be just as efficient as vertical farms – and a lot easier to implement.

In fact, two companies are already working on that approach. Gotham Greens is producing pesticide-free lettuce and basil for restaurants and retailers from rooftop greenhouses in Brooklyn, while Lufa Farms grows 23 veggie varieties in a 31,000 foot greenhouse atop a Montreal office building.

But for the island of Singapore, where real estate is a premium, vertical farming might be the most viable option. "Singapore could be a special case, where land value is so exceptional high, that you have no choice but to go vertically," Giacomelli says.

The Sky Greens vegetables are "flying off the shelves," reports Channel NewsAsia — perhaps because the vertical veggies are fresher than most available in Singapore, which imports most of its produce from China, Malaysia and the U.S. They do, however, cost about 5 to 10 percent more than regular greens.

"The prices are still reasonable and the vegetables are very fresh and very crispy," Rolasind Tan, a consumer, told Channel NewsAsia. "Sometimes, with imported food, you don't know what happens at farms there."

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.